Astronomy Colloquium / Spring 2008

March 12

Dr. Edo Berger

Princeton

Magnetic Activity in Low Mass Stars and Brown Dwarfs - Exploring the Nature of the Dynamo.

Abstract: In recent years the stellar mass function has been extended beyond the sub-stellar boundary with the discovery of numerous brown dwarfs (spectral types L and T). Despite significant observational and theoretical progress, several fundamental questions regarding the structure and formation of these objects remain unanswered. One of the most important questions is whether and how these objects generate, amplify, and dissipate magnetic fields, and how these fields influence the coronae and chromospheres. The answer will provide a window into the properties of the internal convection and the structure of outer atmosphere. Early observations pointed to a breakdown of the solar-type dynamo in late-M dwarfs, and the cessation of magnetic activity. In this talk I will present recent observations, primarily in the radio band, that conclusively point to the presence of large-scale kilogauss magnetic fields. I will further discuss detailed multi-wavelength observations that point to rotation as the key parameter in determining the properties of the fields.